Generally, inductive power transmission systems are frequently used in many applications. They allow powering of devices or charging of batteries (or capacitors) without electrical contacts.
An inductive power transmission system is realized with the help of inductive coupling, e.g. known from WO 2008/050260. Such a system in general comprises a transmitter (also referred to as “transmitting device”) comprising at least one transmitter coil (also referred to as primary coil) which can be energized, thereby generating an alternating magnetic field. The inductive power system further comprises a receiver (also referred to as “receiving device”) that is to be charged or powered. In order to receive power, the receiver is provided with a receiver coil (also referred to as secondary coil) coupled with the transmitter coil. The alternating magnetic field provided by the at least one transmitter coil will induce a voltage in the receiver coil. This voltage can drive a load of the receiver, e.g. charge a battery or light a lamp or power a mobile device.
Normally, in order to save power, when the transmitter does not transmit power to any receiver, the transmitter will be set to standby mode which can also be referred to as “sleeping mode” or “inactive mode”. In the standby mode, the whole transmitter is powered off or at least most of the components are powered off. When the transmitter is in the standby mode, to initiate a power transmission, for example, the transmitter or a detection unit of the transmitter can be powered on regularly for detecting the presence of a receiver; and upon the detection of a receiver, the transmitter will be activated to communicate with the receiver and verify the receiver. If the receiver is a valid device, the transmitter will start the power transmission. On the contrary to the “standby mode”, the status in which the transmitter is powered on for communicating with the receiver and/or transmitting power to the receiver is referred to as “activated mode”.
There might be a situation in which a receiver is positioned on a transmitter for a considerable length of time without requesting power. The transmitter needs to be activated on a regular basis so as to check if the receiver needs power. It can save power by applying long time-intervals, e.g. 5 minutes or longer, for checking if the device needs power. This is not convenient if the user or the application requires fast or instantaneous activation of the wireless power. The user for example might want to have his mobile phone completely charged as long as it is positioned on the transmitter. If a call comes in, the mobile phone starts consuming power from its battery. If the hands-free mode is turned on, the power consumption will increase. In this case the transmitter has to be activated quickly to prevent the battery from becoming partly discharged.
Another example is a device that requires direct power and that has no, or only a small, battery or the like for storing energy. For example, the device might be a lamp or the like, which is switched-on by the user. In that case, the receiver has to be activated instantaneously.